Why snake's tongue is in two parts?

Snakes use their senses to hunt, escape danger, and to find a mate. Since most snakes have poor eyesight their other senses need to make up for it. Snakes don't have noses like we do.  They have nostrils to breathe with but snakes smell with their tongues.  When a snake sticks out its tongue it smells its surroundings.  The moist tongue collects scents and small organisms from whatever it touches and from the air around it. The first half of the snake tongue gives information about the animal odour and the next half gives information about the distance that animal is from snake.  When the tongue goes back into the mouth the forks touches a special sensory organ called the Jacobson's organ on the roof of the mouth and tells the snake what it smells.  Snakes have a small notch in their lips that they can stick their tongues through so they don’t need to open their mouths. Snakes can absorb vibrations through the ground and determine the size of the prey or danger by its movements.